AC LED lamp involving an LED string having separately shortable sections
First Claim
1. An integrated circuit comprising:
- a first terminal;
a second terminal;
a power switch coupled to selectively couple the first and second terminal;
a control circuit adapted to control the power switch based at least in part on an electrical characteristic of a string of Light Emitting Diodes (LEDs) external to the integrated circuit and an input voltage, wherein during a first time a current flows through the power switch, wherein during a second time the current does not flow through the power switch, and wherein the input voltage during the second time is higher than the input voltage during the first time; and
a protection switch, wherein the string of LEDs has a first end node and a second end node, wherein an AC voltage signal having a waveform substantially identical to a waveform of a rectified AC sine wave is present across the string of LEDs between the first and second end nodes, wherein the protection switch is coupled to the second end node, wherein the string of LEDs consumed power, and wherein when an LED string current flows through all of the LEDs of the string of LEDs the protection switch limits the LED string current so as to reduce a power consumed by the string of LEDs while an AC voltage signal is at a maximum.
1 Assignment
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Accused Products
Abstract
An LED lamp includes a rectifier, an integrated circuit and a string of series-connected LEDs. The lamp receives an incoming AC signal such that a rectified version of the signal is present across the LED string. The integrated circuit includes a plurality of power switches. Each power switch is coupled so that it can separately and selectably short out a corresponding one of several groups of LEDs in the string. As the voltage across the string increases the integrated circuit controls the power switches such that the number of LEDs through which current flows increases, whereas as the voltage across the string decreases the integrated circuit controls the power switches such that the number of LEDs through which current flows decreases. LED string current flow is controlled and regulated to provide superior efficiency, reliability, anti-flicker, regulation against line voltage variations, power factor correction, and lamp over-voltage, over-current, and over-temperature protection.
65 Citations
32 Claims
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1. An integrated circuit comprising:
- a first terminal;
a second terminal;
a power switch coupled to selectively couple the first and second terminal;
a control circuit adapted to control the power switch based at least in part on an electrical characteristic of a string of Light Emitting Diodes (LEDs) external to the integrated circuit and an input voltage, wherein during a first time a current flows through the power switch, wherein during a second time the current does not flow through the power switch, and wherein the input voltage during the second time is higher than the input voltage during the first time; and
a protection switch, wherein the string of LEDs has a first end node and a second end node, wherein an AC voltage signal having a waveform substantially identical to a waveform of a rectified AC sine wave is present across the string of LEDs between the first and second end nodes, wherein the protection switch is coupled to the second end node, wherein the string of LEDs consumed power, and wherein when an LED string current flows through all of the LEDs of the string of LEDs the protection switch limits the LED string current so as to reduce a power consumed by the string of LEDs while an AC voltage signal is at a maximum. - View Dependent Claims (2)
- a first terminal;
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3. An integrated circuit comprising:
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a first terminal; a second terminal; a third terminal; a first power switch coupled to selectively couple the first and second terminal; a second power switch coupled to selectively couple the second and third terminal; a current sense resistor; and a control circuit adapted to control the first and second switches based at least in part on the electrical characteristic of a string of Light Emitting Diodes (LEDs) external to the integrated circuit, wherein during a first time a current flows out of the first terminal and onto a first interconnection node on the string of LEDs, wherein during a second time a current flows out of the second terminal and onto a second interconnection node on the string of LEDs, wherein during a third time a current flows out of the third terminal and onto a third interconnection node on the string of LEDs, wherein the control circuit is adapted to control the first and second switches in a condition in which a first number N of LEDs is coupled in series between the current sense resistor and the first interconnection node, in which a second number 2N of LEDs is coupled in series between the first interconnection node and the second interconnection node, in which a third number 4N of LEDs is coupled in series between the second interconnection node and the third interconnection node, and in which a fourth number 8N of LEDs is coupled to the third interconnection node opposite the third number 4N of LEDs, and wherein N is a positive nonzero integer. - View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A system comprising:
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a string of series-connected Light Emitting Diodes (LEDs); an integrated circuit comprising; a first terminal coupled to .a first node on the string of LEDs; a second terminal coupled to a second node on the string of LEDs; a third terminal coupled to a third node on the string of LEDs; a first power switch coupled to selectively couple the first and second terminals; a second power switch coupled to selectively couple the second and third terminals; a protection switch; and a control circuit that controls the first and second power switches; a first input power node; and a second input power node, wherein a current flows from the first input power node, through an amount of the string of LEDs as controlled by the integrated circuit, through the protection switch, and to the second input power node, wherein a rectified AC voltage is present across the string of LEDs, wherein the string of LEDs consumes power, and wherein when the current flows through all of the LEDs of the string of LEDs the protection switch limits the current so as to reduce a power consumed by the string of LEDs while the rectified AC voltage is at a maximum. - View Dependent Claims (20, 21, 22, 23, 24)
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25. A method comprising:
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controlling a number of Light Emitting Diodes (LEDs) of a string of series-connected LEDs through which a current flows from a first node to a second node, wherein a changing voltage signal is present between the first node and the second node, wherein the number increases as a voltage amplitude of the changing voltage signal increases, wherein the number decreases as the voltage amplitude of the changing voltage signal decreases, and wherein the number is made to have at least two discrete different nonzero values as the voltage amplitude of the changing voltage signal changes; and limiting the current flowing through the string of LEDs using a protection transistor, wherein the protection transistor is disposed in series with the string of LEDs, wherein the string of LEDs consumes power, and wherein when the current flows through all of the LEDs of the string of LEDs the protection transistor limits the current so as to reduce the power consumed by the string of LEDs while the voltage amplitude is at a maximum. - View Dependent Claims (26, 27, 28, 29, 30, 31, 32)
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Specification